Maximizing lumber use: The effect of manufacturing defects on yield, a case study

This study analyzed the effect of lumber manufacturing defects on part yield for different lumber grades, lumber lengths, and cutting orders in the furniture industry. The defects investigated were spike marks, conveyer marks, pressure roller stain, drying checks, machine gouge, and machine burn in terms of their occurrence, size, and impact on yield. A database of 5,574 board feet of random width and length white birch boards and two cutting orders were used to conduct rip-first simulation. Boards came from two sawmills, one processing conventional-length logs and the other processing short-length logs. Drying checks had the largest impact on yield, reducing yield by 5.9 percent for one cutting order and 6.4 percent for the second cutting order. The average yield reduction for No. 2A Common lumber was 9.6 percent, vs. 6.6 percent for No. 1 Common and 3.2 percent for Selects lumber. No. 2A Common lumber yields were most affected due to inherent physiological properties that are more common in this grade of lumber, i.e., presence of heartwood and juvenile wood, which make drying more difficult. Spike marks lower yield by about 3 percent for both cutting orders, but they occur only in lumber manufactured at mills using ring debarkers, and mostly on high-grade external boards. Pressure roller stain affected yield by less than 2 percent, and affected smaller sized boards because the defect location offers less flexibility to cut the defect out in the rough mill. Machine burn reduced yield by about 0.6 percent for each of the cutting orders, and it appears to affect conventional-length lumber more due to the dynamics of handling longer boards. Conveyer marks reduced yield by about 0.7 percent. Machine gouge affected yield by 0.5 percent, and most strongly affected yields from short-length lumber.

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